1. Field of the Invention
The present invention relates to a variable valve control apparatus and a variable valve control method for an internal combustion engine, and in particular to a technology for controlling an amount of working medium by variably controlling an operating characteristic of an intake valve.
2. Related Art of the Invention
Heretofore, there has been known an apparatus in which a target torque is set based on an accelerator opening and an engine rotation speed, and an operating characteristic of an intake valve is varied so that a target intake air amount equivalent to the target torque can be obtained (refer to Japanese Unexamined Patent Publication No. 6-272580).
Further, there has also been known a variable valve event and lift mechanism that successively varies valve lifts of engine valves together with operating angles of the engine valves (refer to Japanese Unexamined Patent Publication No. 2001-012262)
Here, since there is a constant correlation between an opening area of the intake valve and a total amount of working medium in a cylinder, it is possible to estimate the total amount of working medium in the cylinder based on the opening area of the intake valve.
Note, the total amount of working medium in the cylinder is the sum of a fresh air amount and a residual gas amount in the cylinder.
Further, the residual gas amount in the cylinder includes a spit-back gas amount to an intake side at the valve overlap time, a spit-back gas amount to the intake side at the intake valve closing time, and further a residual gas amount which has not been discharged via an exhaust valve to remain in the cylinder.
In a region where the opening area of the intake valve is large, a gas temperature in the cylinder rises with an increase of residual gas, and volume efficiency is lowered with the rise of gas temperature.
Accordingly, in the region where the opening area of the intake valve is large, the total amount of working medium in the cylinder is changed to decrease relative to an increase of opening area.
Therefore, in the region where the opening area of the intake valve is large, two opening areas exist corresponding to the total amount of inner-cylinder working medium.
Here, if it is regarded that the total amount of inner-cylinder working medium is not changed relative to the increase of opening area, it is possible to determine the number of opening areas corresponding to the total amount of inner-cylinder working medium to 1.
However, there is caused a problem of the occurrence of control error, if it is regarded that the total amount of inner-cylinder working medium is not changed relative to the increase of opening area.
Further, a correlation between the opening area of the intake valve and an intake valve passing gas amount exists for each effective cylinder capacity that is changed depending on closing timing of the intake valve.
Accordingly, in a system which controls an intake air amount using a variable valve mechanism that successively varies a valve lift and a valve operating angle, it is required to prepare a table indicating the correlation between the opening area ad the valve passing gas amount for each effective cylinder capacity (closing timing of the intake valve).
However, if the table indicating the opening area and the valve passing gas amount is prepared for each effective cylinder capacity, large storage capacity is required and also a large number of processes is required for matching each table.